Transformers are used for converting voltages and currents in electrical circuits and power systems. They are essential components for power system protection and control. Where a voltage or current is too large to be conveniently used by an instrument, it can be scaled down to a standardized low value. Furthermore, transformers can provide galvanic isolation for measurement, protection and control circuitry from the high currents or voltages present on the circuits being measured or controlled.
Such a transformer is only capable of providing linear signal transfer in a limited range, which means that a transformer must be carefully designed for its intended use so that it operates in a linear region. However, under some circumstances, the amplitude of the voltage supplied to the transformer may be chosen below the linear range. This may happen because stronger signals that may occasionally occur must not overload the transformer and there is a limit to the design possibilities. The low signal amplitude results in non-linear magnetization current through a transformer connected in the measurement chain. Consequently, the non-linear magnetization current makes the transformer operate in a non-linear region, leading to inaccurate measurement. This will become worse when such a non-linearity behavior is propagating in a measurement circuit comprising several transformers.
U.S. Pat. No. 5,369,355 discloses a method and a system for linearizing the performance of electrical transformers using negative feedback. A circuit arrangement is configured to compensate a three-winding transformer by using negative feedback generated by an operational amplifier to result in an improved low-end frequency response, reduced harmonic distortion, and substantially resistive input and output impedances.
However, both solutions are expensive due to the auxiliary or the negative feedback circuit arrangements.